The present invention relates to an improved check valve and, more particularly, an improved check valve for use in positive displacement subsurface pumps used in the petroleum industry for pumping crudes having a high degree of suspended solids.
Typical positive displacement pumps used in oil well pumping for pumping crudes employ check valves comprising a valve seat onto which a ball rests and seals against the seat. In a typical well pump, at least one check valve is located in the pump piston and a second check valve is positioned at the fluid inlet to the pump cylinder in which the piston is displaced so as to permit the flow of the pump fluid only in one direction. A typical valving arrangement of the kind discussed above is shown in U.S. Pat. No. 4,018,547 which disclosure thereof is incorporated herein by reference.
When pumping heavy crudes characterized by high contents of suspended solids there is a problem with wear on the valve ball and the valve seat which limits the effective life of the check valves. This wear is due to the effects of erosion caused by the suspended particles in the pumped fluid. In particular, as the valve ball moves closer to the valve seat, the velocity of the pumped fluid increases thereby increasing the likelihood of damage to the valve ball and valve seat by the suspended particles. When the valve ball and valve seat are damaged leakage of the pumped fluid will occur through the valve which results in a loss in volumetric efficiency of the pump and loss of production time when repair of the valve is necessary. Damage to the valve ball, while not desirable, is not as critical as damage to the valve seat. When the valve ball is damaged leakage tends to be minimal as the likelihood of the valve ball, which freely rotates, to seal on the valve seat exactly at the point of damage is low. However, if the valve seat itself is damaged then leakage through the valve might tend to be continuous. By making the valve ball out of a material which is characterized by high resiliency, that is, a modulus of elasticity of between 0.1.times.10.sup.6 psi to 15.times.10.sup.6 psi, the valve ball will tend to rest on the valve seat by elastically deforming. Therefore, even damage to the valve seat would not allow for continuous leakage as was the case with the prior art.
Accordingly, it is a principal object of the present invention to provide a ball check valve for use in positive displacement subsurface pumps used in the petroleum industry for pumping crudes which is less susceptible to damage by impact and erosion due to suspended solids in the pumped fluid.
It is a particular object of the present invention to provide a ball check valve wherein the valve seat comprises a hollow cylindrical body provided with an insert at the orifice of the body which forms the valve seat.
It is a further object of the present invention to provide a ball check valve as set forth above wherein the insert is formed of a material having a hardness greater than the hardness of the valve ball.
It is a still further object of the present invention to provide a ball check valve as described above wherein the valve ball is formed of a material having a high resilience, a modulus of elasticity of between 0.1.times.10.sup.6 psi to 15.times.10.sup.6 psi and a surface hardness greater than the hardness of the hollow cylindrical body.
Further objectw and advantages of the present invention will appear hereinbelow.